1. Field of the Invention
The invention relates to centrifugation bowls for separating blood and other biological fluids. More specifically, the present invention relates to a centrifugation bowl having an improved core that aids in separating and harvesting individual blood components from whole blood.
2. Background Information
Human blood predominantly includes three types of specialized cells (i.e., red blood cells, white blood cells, and platelets) that are suspended in a complex aqueous solution of proteins and other chemicals called plasma. Although in the past blood transfusions have used whole blood, the current trend is to collect and transfuse only those blood components or fractions required by a particular patient. This approach preserves the available blood supply and in many cases is better for the patient, since the patient is not exposed unnecessarily to other blood components and the risks of infection or adverse reaction that may be attendant with those other components. Among the more common blood fractions used in transfusions, for example, are red blood cells and plasma. Plasma transfusions, in particular, are often used to replenish depleted coagulation factors. Indeed, in the United States alone, approximately two million plasma units are transfused each year. Collected plasma is also pooled for fractionation into its constituent components, including proteins, such as Factor VIII, albumin, immune serum globulin, etc.
One method of separating whole blood into its various constituent fractions, including plasma, is xe2x80x9cbagxe2x80x9d centrifugation. According to this process, one or more units of anti-coagulated whole blood are pooled into a bag. The bag is then inserted into a lab centrifuge and spun at very high speed, subjecting the blood to many times the force of gravity. This causes the various blood components to separate into layers according to their densities. In particular, the more dense components, such as red blood cells, separate from the less dense components, such as white blood cells and plasma. Each of the blood components may then be expressed from the bag and individually collected.
Another separation method is known as bowl centrifugation. U.S. Pat. No. 4,983,158 issued Jan. 8, 1991 to Headley (xe2x80x9cthe ""158 patentxe2x80x9d) discloses a centrifuge bowl having a seamless bowl body and an inner core including four peripheral slots located at the top of the core. The centrifuge bowl is inserted in a chuck which rotates the bowl at high speed. Centrifugation utilizing this device is accomplish by withdrawing whole blood from a donor, mixing it with anticoagulant and pumping it into the rotating centrifuge bowl. The more dense red blood cells are forced radially outward from the bowl""s central axis and collected along the inner wall of the bowl. The less dense plasma is displaced inwardly toward the core and allowed to escape through the slots. The plasma is forced through an outlet of the bowl and is separately collected.
The centrifugation bowl of the ""158 patent can also be used to perform apheresis. Apheresis is a process in which whole blood is withdrawn from a donor and separated and the blood components of interest are collected while the other blood components are retransfused into the donor. By returning some blood components to the donor (e.g., red blood cells), greater quantities of other components (e.g., plasma) can generally be collected.
Despite the centrifugation system""s generally high separation efficiency, the collected plasma can nonetheless contain some residual blood cells. For example, in a disposable harness utilizing a blow-molded centrifuge bowl, the collected plasma typically contains from 0.1 to 30 white blood cells and from 5,000 to 50,000 platelets per need to keep the bowl""s filling rate in excess of 60 milliliters per minute (ml/min.) to minimize the collection time, thereby causing slight re-mixing of blood components within the bowl.
Another method of separating whole blood into its individual components is membrane filtration. Membrane filtration processes typically incorporate either internal or external filter media. U.S. Pat. No. 4,871,462 issued to Baxter (xe2x80x9cthe ""462 patentxe2x80x9d) provides one example of a membrane filtration system using an internal filter. The device of the ""462 patent includes a filter having a stationary cylindrical container that houses a rotatable, cylindrical filter membrane. The container and the membrane cooperate to define a narrow gap between the side wall of the container and the filter membrane. Whole blood is introduced into this narrow gap during apheresis. Rotation of the inner filter membrane at sufficient speed generates so-called Taylor vortices in the fluid. The presence of Taylor vortices basically causes shear forces that drive plasma through the membrane, while sweeping red blood cells away.
The prior art membrane filtration devices can often produce a purer blood product, i.e., a blood fraction (e.g., plasma) having fewer residual cells (e.g., white blood cells). However, they typically comprise many intricate components some of which can be relatively costly, making them complicated to manufacture and expensive to produce. Prior art centrifugation devices, conversely, are typically less expensive to produce because they are often simpler in design and require fewer parts and/or materials. Such devices, however, may not produce blood components having the same purity characteristics as membrane filtration devices.
Centrifugation and membrane filtration can also be combined into a single blood processing system. FIG. 1, for example, illustrates a bowl centrifugation system 100 that also includes an external filter medium 142. The system 100 includes a disposable harness 102 that is loaded onto a blood processing machine 104. The harness 102 includes a phlebotomy needle 106 for withdrawing blood from a donor""s arm 108, a container of anti-coagulant solution 110, a temporary red blood cell (RBC) storage bag 112, a centrifugation bowl 114, a primary plasma collection bag 116 and a final plasma collection bag 118. An inlet line 120 couples the phlebotomy needle 106 to an inlet port 122 of the bowl 114, and an outlet line 124 couples an outlet port 126 of the bowl 114 to the primary plasma collection bag 116. A filter 142 is disposed in a secondary outlet line 144 that couples the primary and final plasma collection bags 116, 118 together. The blood processing machine 104 includes a controller 130, a motor 132, a centrifuge chuck 134, and two peristaltic pumps 136 and 138. The controller 130 is operably coupled to the two pumps 136 and 138 and to the motor 132 which, in turn, drives the chuck 134.
In operation, the inlet line 120 is fed through the first peristaltic pump 136 and a feed line 140 from the anti-coagulant 110, which is coupled to the inlet line 120, is fed through the second peristaltic pump 138. The centrifugation bowl 114 is also inserted into the chuck 134. The phlebotomy needle 106 is then inserted into the donor""s arm 108 and the controller 130 activates the two peristaltic pumps 136, 138, thereby mixing anticoagulant with whole blood from the donor, and transporting anti-coagulated whole blood through inlet line 120 and into the centrifugation bowl 114. Controller 130 also activates the motor 132 to rotate the bowl 114 via the chuck 134 at high speed. Rotation of the bowl 114 causes the whole blood to separate into discrete layers by density. In particular, the denser red blood cells accumulate at the periphery of the bowl 114 while the less dense plasma forms an annular ring-shaped layer inside of the red blood cells. The plasma is then forced through an effluent port (not shown) of the bowl 114 and is discharged from the bowl""s outlet port 126. From here, the plasma is transported by the outlet line 124 to the primary plasma collection bag 116.
When all the plasma has been removed and the bowl 114 is full of RBCs, it is typically stopped and the first pump 136 is reversed to transport the RBCs from the bowl 114 to the temporary RBC collection bag 112. Once the bowl 114 is emptied, the collection and separation of whole blood from the donor is resumed. At the end of the process, the RBCs in the bowl 114 and in the temporary RBC collection bag 112 are returned to the donor through the phlebotomy needle 106. The primary plasma collection bag 116, which is now full of plasma, is then processed. In particular, a valve (not shown) is opened allowing plasma to flow through the secondary outlet line 144, the filter 142, and into the final plasma collection bag 118.
Although the combined system of FIG. 1 may produce a purer blood product as compared to conventional centrifugation, it is far more expensive to manufacture.
Briefly, the present invention is directed to a centrifugation bowl with a rotating core having a novel configuration. The centrifugation bowl includes a rotating bowl body which defines a primary separation chamber. A stationary header assembly is mounted on top of the bowl body through a rotating seal. The stationary header assembly includes an inlet port for receiving whole blood and an outlet port from which one or more blood components are withdrawn. The inlet port is in fluid communication with a feed tube that extends into the primary separation chamber. The outlet port is in fluid communication with an effluent tube that extends into the bowl body. The effluent tube includes an entryway at a first radial position relative to a central, rotating axis of the bowl. The core, which is generally cylindrically shaped, is also disposed within the bowl body and defines a secondary separation chamber therein. The core or at least a portion thereof is arranged at a second radial position that is outboard from the entryway to the effluent tube and includes one or more passageways for providing fluid communication between the primary and secondary separation chambers.
In accordance with the present invention, the core has a sealed region at its upper edge relative to both the header assembly and the core""s attachment point to the bowl. The sealed region is free of any perforations, slots or holes and extends a substantial axial length of the core, e.g., one-quarter or more of the core""s length. Adjacent to the sealed region is a fluid transfer region, which may extend the remaining length of the core, e.g., three-quarters of the core""s length. The one or more passageways, which in the preferred embodiment are circular holes, are located in the fluid transfer region of the core. By incorporating an the upper solid region, which is free of any perforations, slots or holes, the upper most passageway through the core is distally positioned relative to the header assembly and the core""s attachment point.
In operation, the bowl is rotated by a centrifuge chuck. Anti-coagulated whole blood is delivered to the inlet port and flows through the feed tube into the bowl body. The centrifugal forces generated within the separation chamber by rotation of the bowl cause the whole blood to separate into its discrete components in the primary separation chamber. In particular, denser red blood cells form a first layer against the periphery of the bowl body and the remaining components, consisting essentially of plasma, which is less dense than red blood cells, form an annular-shaped second layer inside of the red blood cell layer. As more whole blood is delivered to the bowl body, the annular-shaped plasma layer closes in on and eventually contacts the core. The plasma layer, including some non-plasma blood components, passes through the passageways in the transfer region of the core and enters the secondary separation chamber.
Within the secondary separation chamber, the same centrifugal forces generated by rotation of the bowl induce further separation of the plasma component from the non-plasma blood components within the core. The plasma separated within the secondary chamber is driven toward the entryway of the effluent tube where it is withdrawn from the bowl. The combination of the sealed and transfer regions of the core help establish a more uniform flow pattern, thereby facilitating further separation of the plasma within the secondary separation chamber. Non-plasma components that entered the secondary separation chamber are preferably kept away from the effluent tube, and may even be forced back into the primary separation chamber through additional passageways in the transfer region of the core. To collect additional blood components beside plasma, rotation of the bowl is continued, thereby permitting platelets, white blood cells and/or red blood cells to be harvested as well.